Device for venting a pump unit

ABSTRACT

A pump unit for the metered delivery of fuel to internal combustion engines. The pump unit comprises a housing which comprises a longitudinal bore. Located in the longitudinal bore is an overflow valve, via which fuel flows back through a channel into a fuel tank. The passage can be opened or closed by a spring-loaded closing element. Fastened to the valve shaft of the overflow valve is a ring fitting. In the longitudinal bore of the housing there is an additional thread section, via which air flows out through vent gaps into a cavity of the ring fitting.

BACKGROUND INFORMATION

In pump units, such as distributor injection pumps of fuel injectionsystems in motor vehicles, for example, it is important to ensure a safeventing of the pump unit. For example, a distributor injection pump isvented when the pump is started. Aside from that, when the fuel tank hasrun empty, air can also be sucked into the distributor injection pumpand must then be allowed to escape from the delivery chambers of thedistributor injection pump before any fuel can be made to flow.

In a conventional fuel injection pump of this type, described in, forexample, German Patent No. DE-OS 25 22 374, recesses in the form ofconnecting cross sections have been machined into the cylindricalsurface of the pump plungers. These recesses extend from the outletorifices of the discharge channel, starting from the side of the pumpworking chamber. The recesses can have a rectangular contour, can havedifferent widths in the peripheral direction of the pump plunger and canalso differ from one another in their axial dimension, i.e., theirlength. The purpose of a configuration of this type is to achieve across-sectional profile that bends during the opening stroke of the pumpplunger. The intent is, after an initially throttled pressure relief, toenlarge the pressure relief cross section via one of the connectingopenings by the addition of the second connecting opening. The purposeof these connection cross sections is, in particular, to eliminate thethrottling effect that occurs at different rotational speeds of the fuelinjection pump. These cutoff bores are provided in particular to adjustthe injected fuel quantity as a function of the rotational speed. Inthis context, one of the connecting cross sections is generally realizedin the form of a throttle slot. One of the requirements forself-igniting internal combustion engines, when they are operating inthe low-load range, and particularly at idle, is that the fuel must beinjected into the combustion chamber in a precisely timed manner, butwith an extended injection period. This method prevents “knocking” ofthe internal combustion engine, which is particularly noticeable whenthe engine is operating at idle. The purpose of the extended injectionperiod is to ensure that the quantity of fuel injected during theignition lag does not become too great, and therefore to ensure that toomuch fuel is not ignited suddenly, which would lead to a sudden increasein pressure which causes knocking.

German Patent No. DE 36 44 150 describes a fuel injection pump forinternal combustion engines. This pump has a pump cylinder which is bothreciprocating and rotates, and can therefore be used as a distributor ofthe fuel delivered to a plurality of pump plungers that supply injectionpoints. The pump plunger delimits a pump working chamber in the pumpcylinder. The quantity of fuel delivered by the pump plunger iscontrolled by varying the opening of an outlet orifice on the pumpplunger periphery of a discharge channel that is located in the pumpplunger and leads from the pump working chamber to a discharge chamberusing an annular slide valve that can be moved axially on the pumpplunger by an injected-fuel quantity regulator inside the dischargechamber. The annular slide valve has a control edge and at least twoconnection cross sections of different shapes situated in the connectionbetween the outlet orifice and the connection to the discharge chambercreated during the pump plunger delivery stroke by the control edge onthe annular slide valve. One of the connection cross sections has areduced cross section that has a throttling action and is connectedfirst with the discharge chamber during the pump plunger delivery strokeand before another non-throttling connection cross section which has alarger cross section.

European Patent No. EP 0 323 984 describes a fuel injection system forinternal combustion engines. This system includes a high-pressure pumpthat delivers a specific quantity of fuel per pump cycle from a pumpworking chamber using a first control valve that is located in a firstdischarge channel, controls a first return quantity, and determines, inparticular, the beginning and end of the delivery of the fuel injection.Also provided are a metering port having a constant cross section, andan electrically controlled second control valve which is connected inseries thereto and is located in a second discharge channel for a secondreturn quantity. An electronic control unit is used to process thecharacteristics of the internal combustion engine and of the fuelinjection pump into the control variables that regulate the injection.In the second discharge channel, a differential-pressure gauge isprovided to measure the quantity and has an element which is flexiblypositioned against a restoring force, and is pressurized against therestoring force on the one hand by the pressure on theworking-chamber-side of the pump upstream of the metering port, and, onthe other hand, by the discharge-side pressure downstream of themetering port. Its excursion is measured by a travel sensor as acharacteristic of the differential-pressure gauge. In the electroniccontrol unit, in addition to the characteristics of thedifferential-pressure gauge and of the second control valve, thequantity of fuel flowing out via the second discharge channel isdetermined in the form of a control value, and the control time of thefirst control valve is modified on the basis of this control value.

SUMMARY

In accordance with an example embodiment of the present invention, theneed for, for example, an additional bypass bore in the overflow valveon a distributor injection pump is eliminated. In overflow valves, thisadditional bypass bore represents an additional working step in thelarge-scale production of the values, which, on the one hand, requiresrepeated chucking of the workpiece in the processing machine in questionand, on the other hand, has a significant influence on the accuracy ofthe calibration of the overflow valve. The approach proposed by thepresent invention enables the bypass bore previously realized in theoverflow valve to be advantageously integrated into the longitudinalbore of the pump housing quite simply from a manufacturing standpoint,by introducing an additionally deepened thread section during thecircular milling of the thread into the housing. This thread section isfabricated in a single work operation process with the female thread inthe longitudinal bore, into which the overflow valve is introduced, thetool moving downward along a helical path during the tensioning process.

The thread section may be introduced into the longitudinal bore of thehousing in such a way that the longitudinal bore runs at an offset,i.e., eccentrically, with respect to the outer flanks of the overflowvalve. As a result of the eccentrically formed thread section, a gapthat runs in a cascade form is created between the female and malethread. This gap forms a defined throttling point.

The thread section, which is manufactured in a single working step inthe female thread of the longitudinal bore of the pump housingpreferably by circular milling, ensures that the air is sucked in fromthe interior of a pump unit, such as a distributor injection pump. Thereis negligible escaping of fuel through the gap between the female andmale threads, because air has a significantly lower viscosity than fueland can therefore escape through the gap between the female and malethreads more easily than fuel.

A ring fitting, which has a cavity, is assigned to the overflow valvewhich is inserted exemplarily into the longitudinal bore of the pumphousing of a distributor injection pump. The cavity of the ring fittingcommunicates via a transverse bore in the valve shaft with thelongitudinal bore of the overflow valve. The ring fitting may be sealedwith respect to the valve shaft of the overflow valve by two sealingwashers, one of which is located in the head region of the overflowvalve and the other opposite a plane surface of the pump housing. Theoutside diameter of the valve shaft in the overflow valve and the insidediameter of the two sealing washers are advantageously coordinated sothat vent gaps are formed, via which an escape of air from the interiorof the pump unit is ensured.

In addition to its use on fuel pump units, for example on distributorinjection pumps, the approach of the present invention may also be usedin pump units for hydraulic fluid, in power steering systems, forexample. The approach of the present invention may also be used ingeneral for low-pressure inlet and outlet lines which are fastened byring fittings and perform a bypass throttling function.

BRIEF DESCRIPTION OF THE DRAWINGS

An example embodiment of the present invention is explained in greaterdetail below with reference to the accompanying drawings.

FIG. 1 is a longitudinal section through an overflow valve integratedinto the housing of a distributor injection pump.

FIG. 1.1 shows the relative position between female thread of thelongitudinal bore and an additional thread section.

FIG. 2 is a plan view of the inner contour of the housing without theoverflow valve illustrated in FIG. 1 screwed in.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a longitudinal section through an overflow valve that isintegrated into the housing of a distributor injection pump.

The housing of a pump such as a distributor injection pump, for example,that delivers a fluid, such as fuel, for example, in direct-injectionand air-compression-type internal combustion engines is identified byreference numeral 1 and delimits an interior space 2 of the pump.Interior space 2 of the pump unit is in communication via a first bore 3with an overflow valve 7 located in a longitudinal bore 4. Overflowvalve 7 may be screwed in via a threaded segment 5 designed as a malethread into a corresponding female thread segment in longitudinal bore4. The threaded connection illustrated in FIG. 1 ensures a connectionbetween overflow valve 7 and housing 1 that is able to withstand eventhe elevated pressures in a distributor injection pump for internalcombustion engines, for example.

In the upper portion of housing 1, a plane surface 6 may be formed,surrounding longitudinal bore 4 in housing 1 in the shape of a ring,into which plane surface a ring 15 made of a soft-metal material whichacts as a first sealing washer may be placed. In the example embodimentillustrated in FIG. 1, first sealing washer 15 created in this manner isinserted as a seal between a ring fitting 15 which surrounds valve shaft14 of overflow valve 7 and plane surface 6 of housing 1 of the pumpunit. Opposite first sealing washer 15, which is made of a soft metalmaterial, a second sealing washer 17, which may also be fabricated froma soft metal material, is set in below head region 13 of overflow valve7, To ensure the required sealed contact and to apply the necessarypreloading force, second sealing washer 17 engages on a plane surface 18on head region 13 of overflow valve 7 and, analogously to first sealingwasher 15, which is accommodated on plane surface 6 of housing 1, isconnected to an outer surface of ring fitting 19.

By screwing overflow valve 7 into female threaded section 5 oflongitudinal bore 4, the preloading force required to create the seal isapplied and ring fitting 19 is fastened to the outside of valve shaft 14of overflow valve 7.

Overflow valve 7 itself includes a passage 8 which is in communicationwith first bore 3 of housing 1 of the pump unit. Passage 8, as afunction of the pressure prevailing in interior space 2 of the housing,may be closed or opened by a closing element 9 that has a sphericalshape. For this purpose, pressure is applied to the spherically shapedclosing element 9 by a coil spring 11 which in turn is supported on acounter-support 12 in head region 13 of overflow valve 7. In the variantof the approach of the present invention illustrated in FIG. 1,counter-support 12 is designed in the form of a ball that has beenshrink-fitted into head region 13 of overflow valve 7. In addition tothe shrink-fitting of a spherically shaped counter-support 12, acounter-support of the spring that acts on spherically shaped closingbody 9 may also be realized in the form of a counter-support that isbolted into the vicinity of head 13 of overflow valve 7.

Spherical closing element 9 closes a valve seat 10 formed in passage 8underneath a transverse bore 20 that runs through the wall of valveshaft 14 of overflow valve 7. As a function of the pressure levelprevailing in pump interior 2, upon reaching a specific pressurelimiting value in passage 8, closing body 9 is lifted by the pressure,counter to the spring action of spring 11, so that fuel is able to flowout of pump interior 2 via transverse bore 20 of overflow valve 7 into acavity, denoted by reference numeral 23, of ring fitting 19, and, fromthere, into the fuel tank (not shown) of a motor vehicle.

Displaced by a distance 22, i.e., an eccentricity, from the center lineof passage 8, a thread section 24 is formed in female thread segment 5of longitudinal bore 4 of housing 1. Because additional thread section24 extends through the threads of the first threaded segment formed inlongitudinal bore 4, and, in this way, forms a channel for the passageof air to the outside of valve shaft 14 of overflow valve 7, the centerof additional thread section 24 is offset by above mentionedeccentricity 22 with respect to the center line of passage 8 in theinterior of valve shaft 14 of overflow valve 7. Thread section 24 isadvantageously fabricated in the same working step as the manufacture offemale thread segment 5 in longitudinal bore 4 of housing 1 of the pumpunit. Circular milling may be considered a preferred fabrication method,so that additional thread section 24 may be fabricated in threads offirst threaded segment 5 of longitudinal bore 4 in housing 1simultaneously with first female thread segment 5 of longitudinal bore4.

The above mentioned sealing washers 15 and 17 are located on both sidesof ring fitting 19 which surrounds the outside periphery of valve shaft14 of overflow valve 7. Inside diameter 16 of first sealing washer 15 isselected in such a way that air may flow via bore 3, along the channelformed between female thread segment 5 of longitudinal bore 4 andadditional thread section 24 on the outside of valve shaft 14 ofoverflow valve 7 toward the first sealing washer. Between insidediameter 16 of first sealing washer 15 and the outside diameter of valveshaft 14, a first vent gap 26 is formed, via which air is able to escapefrom pump interior 2. The fuel cannot escape because of the small sizeof vent gap 26. The escape of fuel is also prevented by closing element9, which is held in its seat 10 by spring element 11. Air may escapefrom pump interior 2 of pump unit 1 even at a significantly lowerpressure level, compared with the overpressure level at which closingelement 9 moves out of its seat 10 on the upper side of passage 8against the action of spring element 11.

In addition to vent gap 26 which is formed between the periphery ofvalve shaft 14 of overflow valve 7 and inside diameter 16 of firstsealing washer 15, there is an additional vent gap 27 between the insidediameter of ring fitting 19 and the outside diameter of valve shaft 14of overflow valve 7. Via this air gap, which is sealed externally due tothe preloading of first sealing washer 15 and of second sealing washer17, the air that escapes from interior space 2 of pump unit 1 flows intocavity 23 of ring fitting 19 and, from there, for example, to a tankvent or directly back into the fuel tank of a motor vehicle.

FIG. 1.1 is a schematic illustration of the configuration and of theposition of the first threaded segment and of the additional threadsection with respect to each other in longitudinal bore 4.

The illustration in FIG. 1.1 shows that a first female thread 5 is cutinto longitudinal bore 4 in housing 1 of the pump unit. An additionalthread section 24 is machined in its threads, using circular milling ina single working step, and for its part, extends through the threads offirst female thread segment 5 inside longitudinal bore 4, so that,viewed along longitudinal bore 4 in the axial direction, a channel isformed, via which any air that is present in interior space 2 of pumpunit 1 may escape. Because the diameter of additional thread section 24is smaller than the diameter of first threaded segment 5 in longitudinalbore 4 of housing 1 of the pump unit, additional thread section 24 isoffset by an eccentricity 22 with respect to the center of firstthreaded segment 5. In terms of the manufacturing requirements,therefore, additional thread section 24 may be fabricated in a singleoperation simultaneously with the manufacture of first threaded segment5—which is realized in a larger tip diameter. In the approach of thepresent invention, the need is eliminated for calibrating bypassopenings in an overflow valve 7, of the type that was necessary onconventional overflow valves, because the bypass opening may beintegrated directly into longitudinal bore 4 of housing 1 of a pumpunit.

FIG. 2 is a plan view of the threaded bore in housing 2.

FIG. 2 shows that overflow valve 7 may be screwed with its firstthreaded segment 5 into a longitudinal bore 4 of housing 1. Threadedsegment 5—which is realized in the form of a male thread in the lowerregion of valve shaft 14 of overflow valve 7—is engaged withcorresponding threaded segment 5 which is realized in the form of afemale thread of longitudinal bore 4 in housing 1, additional threadsection 24 between the male thread of valve shaft 14 and female threadsegment 5 of longitudinal bore 4 creating a channel that permits theescape of air, which channel however is sealed externally by firstsealing washer 15 which is placed into plane surface 6 of housing 1. Itis thereby possible for the air to flow out of the interior via ventgaps 26 and 27 illustrated in FIG. 1 into interior 23 of ring fitting 19surrounding valve shaft 14 and, from there, into the vehicle tank or atank vent.

The eccentricity 22 by which additional thread section 24 is offset withrespect to the center of female thread 5 of longitudinal bore 4 is alsoidentified by reference number 22 in FIG. 2. Eccentricity 22 resultsfrom the realization of additional thread section 24 in a smaller tipdiameter compared with the diameter of female thread 5 in longitudinalbore 4 of housing 1, for example of a distributor injection pump forair-compression-type internal combustion engines. In addition to its usefor venting distributor injector pumps, which can be necessary when thetank of a motor vehicle is run completely empty and when distributorinjection pump 1 is started, the method proposed by the presentinvention for venting a pump interior may also be used in hydraulicfluid pumps in motor vehicles, such as in a power steering system, forexample. The approach proposed by the present invention for venting thepump interior may also be used in fuel pump units for diesel fuel, aswell as for gasoline.

The method proposed by the present invention for venting a pump interior2 of a pump unit enables the circular milling manufacturing method to beused to machine the vent channel that functions as a bypass intolongitudinal bore 4 of housing 1. This eliminates the need for formingan additional bypass bore in overflow valve 7 which is screwed intolongitudinal bore 4 on housing 1. As a result, it is possible to reducethe number of rejects during the installation of overflow valves 7 inthe pump unit, because the influence of the bypass bore is eliminatedand this additional processing step in the manufacture of overflowvalves 7 in series production may be eliminated. The bypass bore isadvantageously realized in an additional thread section 24 that may bemanufactured in a single operation with the machining of female threadsegment 5 in a longitudinal bore 4 in housing 1 of the pump unit inquestion.

1. A pump unit for metered delivery of fuel for an internal combustionengine comprising: a housing which surrounds an interior space andincludes a longitudinal bore; an overflow valve arranged in thelongitudinal bore and via which fuel flows back through a passage into afuel tank, the passage being able to be closed or opened by aspring-loaded closing element; and a ring fitting held on a periphery ofthe overflow valve, wherein a thread section is formed in thelongitudinal bore of the housing, via which air can escape via vent gapsinto a cavity of the ring fitting, wherein the thread section is formedin a first female thread segment to receive the overflow valve of thelongitudinal bore.
 2. The pump unit as recited in claim 1, wherein acenter of the thread section is located at an offset from a center ofthe first female thread segment in the longitudinal bore.
 3. The pumpunit as recited in claim 1, wherein the thread section in the firstfemale thread segment is one of fabricated by circular milling, orfabricated in an additional operation.
 4. The pump unit as recited inclaim 1, further comprising: sealing washers, wherein between aperipheral surface of a valve shaft of the overflow valve and thesealing washers on the valve shaft, the vent gaps are realized, viawhich air escaping from an interior space of the pump unit flows outinto the ring fitting via the thread section of the longitudinal bore.5. The pump unit as recited in claim 1, wherein the overflow valve has apassage and a transverse bore which is in communication with the cavityof the ring fitting, the passage being closed by the closing element,and being opened as a function of pressure in the interior space of thehousing.
 6. A pump unit for metered delivery of fuel for an internalcombustion engine comprising: a housing which surrounds an interiorspace and includes a longitudinal bore; sealing washers; an overflowvalve arranged in the longitudinal bore and via which fuel flows backthrough a passage into a fuel tank, the passage being able to be closedor opened by a spring-loaded closing element; and a ring fitting held ona periphery of the overflow valve, wherein a thread section is formed inthe longitudinal bore of the housing, via which air can escape via ventgaps into a cavity of the ring fitting, wherein between a peripheralsurface of a valve shaft of the overflow valve and the sealing washerson the valve shaft, the vent gaps are realized, via which air escapingfrom an interior space of the pump unit flows out into the ring fittingvia the thread section of the longitudinal bore, and wherein the ventgaps are defined by respective inside diameters of a first one of thesealing washers and a second one of the sealing washers.
 7. A pump unitfor metered delivery of fuel for an internal combustion enginecomprising: a housing which surrounds an interior space and includes alongitudinal bore; sealing washers; an overflow valve arranged in thelongitudinal bore and via which fuel flows back through a passage into afuel tank, the passage being able to be closed or opened by aspring-loaded closing element; and a ring fitting held on a periphery ofthe overflow valve, wherein a thread section is formed in thelongitudinal bore of the housing, via which air can escape via vent gapsinto a cavity of the ring fitting, wherein between a peripheral surfaceof a valve shaft of the overflow valve and the sealing washers on thevalve shaft, the vent gaps are realized, via which air escaping from aninterior space of the pump unit flows out into the ring fitting via thethread section of the longitudinal bore, and wherein a first one of thesealing washers is placed into a plane surface that is adjacent to thelongitudinal bore in the housing.
 8. A pump unit for metered delivery offuel for an internal combustion engine comprising: a housing whichsurrounds an interior space and includes a longitudinal bore; sealingwashers; an overflow valve arranged in the longitudinal bore and viawhich fuel flows back through a passage into a fuel tank, the passagebeing able to be closed or opened by a spring-loaded closing element;and a ring fitting held on a periphery of the overflow valve, wherein athread section is formed in the longitudinal bore of the housing, viawhich air can escape via vent gaps into a cavity of the ring fitting,wherein between a peripheral surface of a valve shaft of the overflowvalve and the sealing washers on the valve shaft, the vent gaps arerealized, via which air escaping from an interior space of the pump unitflows out into the ring fitting via the thread section of thelongitudinal bore, and wherein a second one of the sealing washers is incontact with a ring-shaped plane surface in a vicinity of a head of theoverflow valve.
 9. A pump unit for metered delivery of fuel for aninternal combustion engine comprising: a housing which surrounds aninterior space and includes a longitudinal bore; an overflow valvearranged in the longitudinal bore and via which fuel flows back througha passage into a fuel tank, the passage being able to be closed oropened by a spring-loaded closing element; a ring fitting held on aperiphery of the overflow valve; and a spring, a counter-support of thespring configured to press against the closing element, thecounter-support being in the form of a sphere that is pressed orshrink-fitted into a head region of the overflow valve, wherein a threadsection is formed in the longitudinal bore of the housing, via which aircan escape via vent gaps into a cavity of the ring fitting, and whereinthe overflow valve has a passage and a transverse bore which is incommunication with the cavity of the ring fitting, the passage beingclosed by the closing element, and being opened as a function ofpressure in the interior space of the housing.